Many machines require filters to separate undesirable substances from fluids traveling at various velocities and under various pressures. Examples of these types of filters include fuel filters, oil filters, vacuum pump discharge filters, and blower discharge filters. These types of filters need to have a design which ensures the filters do not interrupt fluid flow when their filter elements become clogged. Failure to allow the fluid to continue to flow could cause these filters or the machines associated with the filters to sustain damage. The damage may result in physical injury to an operator of the machine.
Industry uses a variety of mechanisms to ensure clogged filter elements do not interrupt fluid flow. Generally, each mechanism functions by creating a bypass to allow the fluid to exit the filter without passing through the filter element. U.S. Pat. No. 3,757,951 (Redenbarger) discloses an inside-out filter having a mechanism to create a bypass. The mechanism includes a compression spring disposed between an exterior of a filter element and an interior of a filter housing. During normal operation, when the filter is in an operational mode, the spring holds the filter element in place over a fluid inlet. The filter element and spring are stabilized relative to each other and relative to the inlet, in part, by a rod extending through both the filter element and spring.
In the operational mode, the fluid flows into the fluid inlet, through the filter element, and out a fluid outlet. However, when the filter element clogs, the fluid exerts force on the filter element. The force exceeds the compression force the spring exerts on the filter element. The filter element thus moves away from the fluid inlet. The movement of the filter element away from the inlet creates the fluid bypass which allows fluid to bypass the filter element and exit the fluid housing outlet without filtration.
The apparatus has disadvantages. First, the bypass mechanism disrupts the flow of the filtered fluid. Also, a user must continually worry about the mechanism's cleanliness. The mechanism may attract debris when the filter moves to the bypass position. If a user fails to clean the debris off the mechanism after changing the filter element, debris may dislodge from the mechanism upon subsequent use of the filter. The debris may damage the machine associated with the filter.
Another disadvantage concerns the burden the mechanism imposes on a user or installer during a change of the filter element. A user must dismantle and reassemble the spring mechanism to change the filter element. The process is cumbersome and may result in the loss of needed parts.
U.S. Pat. No. 3,993,561 (Swearingen) provides another example of a filter having a bypass mechanism. Swearingen, like Redenbarger, holds the filter element in place with a compression spring. The compression spring is between an exterior of the filter element and an interior of the housing. Swearingen has a plurality of fluid outlets coaxially surrounding the spring. Swearingen, however, still requires a central outlet. The spring mechanism is between the central outlet and the filter element. Thus, the spring would appear to disrupt fluid traveling from the filter element to the outlet.
Swearingen's mechanism has the drawback of clumsy installation. A user has to remove and reinstall the spring after each change. Additionally, sediment could build up on the spring when the filter element is in the bypass position. The sediment could come loose upon subsequent use of the filter. The loose sediment could damage the machine associated with the filter. Additionally, the filter element only has a spring stabilizing its one end. The filter element thus may suffer from wobble as fluid flows.
Some have tried to solve the problems of clumsy installation and fluid disruption by developing filter elements having built-in release valves. U.S. Pat. No. 4,689,144 discloses an example of a filter element with a built-in release valve. The built-in release valve, however, has the drawback of increasing the cost of the disposable filter element.